ssa  R Documentation 
Main interface function to the implemented SSA methods. Runs a
single realization of a predefined system. For a detailed explanation
on how to set up your first SSA system, check the introduction
vignette: vignette("an_introduction", package = "GillespieSSA2")
.
If you're transitioning from GillespieSSA to GillespieSSA2,
check out the corresponding vignette:
vignette("converting_from_GillespieSSA", package = "GillespieSSA2")
.
ssa( initial_state, reactions, final_time, params = NULL, method = ssa_exact(), census_interval = 0, stop_on_neg_state = TRUE, max_walltime = Inf, log_propensity = FALSE, log_firings = FALSE, log_buffer = FALSE, verbose = FALSE, console_interval = 1, sim_name = NA_character_, return_simulator = FALSE )
initial_state 

reactions 
A list of reactions, see 
final_time 

params 

method 

census_interval 

stop_on_neg_state 

max_walltime 

log_propensity 

log_firings 

log_buffer 

verbose 

console_interval 

sim_name 

return_simulator 
Whether to return the simulator itself, instead of the output. 
Substantial improvements in speed and accuracy can be obtained by
adjusting the additional (and optional) ssa
arguments. By default
ssa
uses conservative parameters (o.a. ssa_exact()
) which prioritise
computational accuracy over computational speed.
Approximate methods (ssa_etl()
and ssa_btl()
) are not fool proof!
Some tweaking might be required for a stochastic model to run appropriately.
Returns a list containing the output of the simulation:
out[["time"]]
: [numeric]
The simulation time at which a census was performed.
out[["state"]]
: [numeric matrix]
The number of individuals at those time points.
out[["propensity"]]
: [numeric matrix]
If log_propensity
is TRUE
, the propensity value of each reaction at each time point.
out[["firings"]]
: [numeric matrix]
If log_firings
is TRUE
, the number of firings between two time points.
out[["buffer"]]
: [numeric matrix]
If log_buffer
is TRUE
, the buffer values at each time point.
out[["stats"]]
: [data frame]
Various stats:
$method
: The name of the SSA method used.
$sim_name
: The name of the simulation, if provided.
$sim_time_exceeded
: Whether the simulation stopped because the final simulation time was reached.
$all_zero_state
: Whether an extinction has occurred.
$negative_state
: Whether a negative state has occurred. If an SSA method other than ssa_etl()
is used, this indicates a mistake in the provided reaction effects.
$all_zero_propensity
: Whether the simulation stopped because all propensity values are zero.
$negative_propensity
: Whether a negative propensity value has occurred. If so, there is likely a mistake in the provided reaction propensity functions.
$walltime_exceeded
: Whether the simulation stopped because the maximum execution time has been reached.
$walltime_elapsed
: The duration of the simulation.
$num_steps
: The number of steps performed.
$dtime_mean
: The mean time increment per step.
$dtime_sd
: THe standard deviation of time increments.
$firings_mean
: The mean number of firings per step.
$firings_sd
: The standard deviation of the number of firings.
GillespieSSA2 for a high level explanation of the package
initial_state < c(prey = 1000, predators = 1000) params < c(c1 = 10, c2 = 0.01, c3 = 10) reactions < list( # propensity function effects name for reaction reaction(~c1 * prey, c(prey = +1), "prey_up"), reaction(~c2 * prey * predators, c(prey = 1, predators = +1), "predation"), reaction(~c3 * predators, c(predators = 1), "pred_down") ) out < ssa( initial_state = initial_state, reactions = reactions, params = params, method = ssa_exact(), final_time = 5, census_interval = .001, verbose = TRUE ) plot_ssa(out)
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